Field of the Invention
The invention relates to a device and method for guiding sheet material in a printing press, particularly in a sheet-fed rotary offset printing press, the device having a guide surface located below a path in which a sheet is guidable, and nozzles arranged in zones within the guide surface, the zones including a first zone extending along a longitudinal axis of the guide surface, and a second and a third zone, respectively, located at the left-hand and right-hand sides of the first zone.
When transporting sheet material through a printing press, in particular, a sheet-fed offset rotary printing press, it is generally necessary to guide the sheet material over given stretches or distances without fluttering and as taut as possible without any breaks or distortions in the taut or stretched disposition thereof. For this purpose, guide surfaces are used having air nozzles arrayed therein through which air is blown against the underside of the sheet, so that the sheet is guided in a floating manner above the guide surface.
The German Published Non-prosecuted Patent Application (DE-OS) 44 06 844 discloses a device for floatingly guiding sheets in a rotary printing press, the device having a guide surface provided with air nozzles arranged in three zones extending in a direction of travel of a sheet and across the entire width of the sheet guide surface, the nozzles being always supplied with air both in one-sided or recto sheet printing as well as in recto/verso or first form and perfector sheet printing modes, thereby assuring reliable flotation of the sheet in either printing or operating mode. To keep the sheet taut simultaneously with the flotation thereof, the nozzles in the center region along the longitudinal axis of the sheet guide surface blow air in a direction substantially opposite to the motion of the sheet and towards the trailing edge of the sheet. This is intended to tauten or apply tension to the sheet in the longitudinal direction of the sheet. The nozzles arranged in the other two lateral zones blow air in a direction substantially towards the side and the trailing edge of the sheet, so that, in these lateral guide zones, the sheet is tautened or subjected to tension both laterally and in the longitudinal direction thereof. This published German patent application does not offer any indication that the nozzles in the center zone blow air in the direction of motion of the sheet, nor that air be applied to or blown through the nozzles in the center zone in the recto/verso printing or operating mode and that the nozzles be shut off in the recto or one-sided sheet printing mode.